Newer-generation magnetic resonance imaging (MRI) systems may generate and transmit a plurality of individual radio-frequency (RF) pulse trains in parallel over different independent radio-frequency transmit channels. Individual RF signals are applied to the individual transmit channels (e.g., individual coil elements such as the individual rods of a whole-body antenna).
Multichannel transmission coils are operated at defined amplitude and phase settings for the individual channels. An instantaneous spatial excitation field results from local complex superposition of HF fields generated by the individual coil elements. Each individual HF field is dependent on the associated coil element, and with increasing field intensity (e.g., 3T), each individual HF field is also increasingly dependent on an object being examined (e.g., the body of a patient).
HF pulse calibration is provided for patient-specific optimization of MR excitation. Spatial excitation maps (e.g., B1 maps) of the individual coil elements are measured. Based on the measured B1 maps of the individual coil elements, amplitudes and phases of transmit voltages for the individual channels (e.g., B1 shims) are calculated, so that the excitation is optimal for a specific patient in terms of a quality criterion.